Ab Initio Models for Electron Tunnelling Between Transition Metal Complexes

Electron transfer matrix elements are calculated and analyzed for several pairs of transition metal complexes of the type ML6 2+-ML6 3+, chosen so as to allow a comparison of t2g(π) vs eg (σ) transfer (M = Fe, Co, and Ru), and NH3 vs H2O ligands, based on an apex-to-apex orientation of the reactant complexes. The magnitude of the calculated matrix elements, which span the range from non-adiabatic to strongly adiabatic coupling, are found to exhibit a pronounced dependence on transfer type (eg > t2g) and ligand type (NH3 > H2O), an effect which is correlated with the degree of mixing of the metal and ligand orbitals, using a simple LCAO-type analysis of the ab initio molecular orbitals.